1. The Field of the Invention.
This invention relates generally to an apparatus for segregating the constituents of scrapped lead-acid storage batteries. More particularly, the invention is concerned with the hydromechanical separation of the components of lead-acid batteries into three distinct categories. (1) grid metal and other lower grade antimonial lead alloys, (2) active material, consisting of elemental lead, lead oxide and lead sulfate and (3) battery cases and separators consisting of organic material. Still more particularly the invention is concerned with combining such physical separation with simultaneous chemical treatment of the lead sulfate and neutralization of the electrolyte in such lead-acid batteries in order to facilite further recovery of the lead values therein.
2. Description of the Prior Art
The recovery of lead and lead components is scrapped lead-acid batteries according to known methods typically involves first draining the batteries to eliminate the electrolyte therein and then crushing, guillotining, or otherwise fragmentizing the batteries to expose their plates. At this point the plates can be treated either by smelting or by mechanical separation of the active material from the girds. The latter technique is preferable not only because smelting is basically an inefficient method resulting in lead losses. but also because it gives rise to serious and potentially dangerous pollution problems.
There are a number of processes and types of apparatus known to the art which are designed to mechanically separate or isolate the constituents of whole or fragmented batteries, and a variety of well known techniques are employed in such processes and apparatus in varying combinations and with varying degrees of complexity.
For example, as exemplified in U.S. Pat. No. 3,561,684, a method and apparatus is disclosed for separating the components of secondary cells comprising means including an impact crusher for breaking up battery cases; vibrating screen equipment for dividing this mass into one fraction which comprises the separators and a second fraction comprising at least the major part of the housing and also the metallic fragments; further impact crusher means including a magnetic separator for removing ferrous material from the separators, further screen means for removing residues of grid lead still adhering to the separators, resonance screen means for additional separation of the second fraction of battery fragments by size, gravity separating means for further division of the smaller particles passing through the resonance screen into grid lead active material and plastic parts, and further gravity means for separating the larger particles of the second fraction into (1) sinkable grid material, some active material and other metallic parts and (2) floatable housing fragments.
The efficiency of such a method is necessarily degraded by the proliferation of equipment which must be employed and the consequent space requirements, as revealed by the flow-chart in this patent.
Obviously, it is desirable in this highly competitive field to devise a method and apparatus for recovering lead values from storage batteries which reduce the initial capital outlay and operating costs to a minimum. Clearly, therefore, an important characteristic of such method and apparatus ought to be the maximum simplicity in processing consistent with the production of lead values of high purity.
A further disadvantage of prior art methods for recovery of lead-acid battery constituents is that it is found necessary to remove substantially all the electrolyte from the battery cells prior to introduction into crushing of fragmentation vessels unless they are made acid resistant, which is ordinarily impractical. For example, in the method of U.S. Pat. No. 3,493,183 battery cells are first delivered to an acid resistant storage area provided with special drainage means for the acid. Subsequently, acid still adhering to the battery fragments is largely removed by a dewatering process. Only then are the fragments ready for mechanical separation to obtain lead values.
In another kown mechanical method of recovery of battery constituents as exemplified in U.S. Pat. No. 1,587,623 grid plates and pasted oxides are crushed together in a ball mill in the presence of water, which serves as a vehicle to flow out the crushed fragments into a screen separator. The oxides suspended in the water are passed through the screen and conducted to settling tanks, while the metal chunks, consisting of antimonial lead, are retained on the screen, washed and collected. This method of course requires that steps be taken elsewhere to extract the grid plates from scrapped batteries, and it is therefore not designed to handle whole or shredded batteries including cases and separators, electrolyte, and other battery parts. Furthermore, since all of the crushed material is passed onto the screen separator with the suspension of active material, the finer particles of grid metal will pass through the screen and contaminate th active material unless the mesh of the screen is made very fine, which in turn increases the probability of blockage of the screen by moist particles.
In a used battery the active material contains a large proportion of lead sulfate which must be removed in order to recover reusable lead values. It is well known that the lead sulfate can be transposed to lead carbonate by chemical reaction with carbonate solutions such as sodium carbonate. In a known process as exemplified in U.S. Pat. No. 2,005,408 such transposition is accomplished in a rotary vessel in which scrap battery plates are tumbled at the same time. The reaction takes place in water at near boiling temperature and requires 30 to 60 minutes for completion. The disadvantage of this method lies in the excessive time and high water temperature necessary for the reaction as well as the fact that it is cyclic process, i.e., not adapted to operate continuously.